Miniature variable resistor



March 27, 1956 w POLYE ETAL 2,740,025

MINIATURE VARIABLE RESISTOR Filed June 19, 1953 FIG. 1

4 |Q 27 5 a a k I i ii 23 4-| I ll \6 IIIEII III IN VEN TORS W/LL/AM R.POLVE United States Patent MINIATURE VARIABLE RESISTOR William R. Polye,River Edge, and Andre P. Viret,

Tenafly, N. L, assignors to Bendix Aviation Corporation, Teterboro, J.,a corporation of Delaware Application June 19, 1953, Serial No. 362,916Claims. (Cl. 201-48) This invention relates to electrical miniaturevariable resistors, such as potentiometers and rheostats, and especiallyto a construction for instruments of this type adapted for effective usein extremely small sizes. Such miniature instruments are desirable forincorporation in small electrical units, such as indicating instruments,where only a very small amount of space is available in the housing.

A feature of the invention is the provision of a variable resistorconstruction whose parts may be readily assembled in sizes so small thatthe usual arrangements are impractical or undesirable. Moreparticularly, the casing is designed for assembly without screws, andthe connection to the contact arm is planned so as to eliminate theusual devices located within the casing, thereby permitting a reductionin casing size. A further feature is the provision of an advantageousarrangement for adjusting the position of the contact arm including asimple structure which insulates the arm from the adjusting element.Another feature is an improved stop arrangement for limiting the travelof the arm.

These and other features of the invention will appear from the followingdescription in conjunction with the accompanying drawings, in which:

Figure l is a vertical central section through an instrument embodyingthe invention;

Figure 2 is a plan view with the cover and adjusting arrangementremoved; and

Figure 3 is a fragmentary vertical section on line 3-3 of Figure 2.

In the illustrated embodiment a housing 1 made of suitable plastic suchas Bakelite or similar insulating material, is provided with a bottom 2,an integral cylindrical side wall 3 and a separable cover 4 tightlyfitting said wall, and advantageously rabbeted at 5, arranged for secureengagement on the wall, as by cementing. A fiat resistance element 6extends around the inner face of wall 3 and is suitably held in place,as by cement. Said element preferably consists of a wire resistancewound on a strip of fishpaper or other suitable sheet insulatingmaterial, when a substantial current is to pass through the instrument,though a strip or layer of carbon or other resistance material may beused where conditions permit. At least one end of the resistance elementis electrically connected to a terminal mounted on the casing. In theform shown, the terminal 7 is in the form of a metal rivet extendingthrough and flanged on both sides of the bottom 2, to which an end ofthe wire 8 of resistance 7 is at tached. Where the instrument is adaptedfor use as a potentiometer, as shown, the other end of wire 8 is alsoconnected to a second similar terminal 7. Said wire ends are preferablycemented to the housing 1 so that they will not become loose.

A contact arm assembly 9 is rotatably mounted in the housing 1. Itincludes a metal spindle 10 having a lower cylindrical reduced endportion 11 extending through a bearing opening in the bottom 2 andhaving a slightly concave end bearing against a convex contact stud 12fixed to a spring arm 13 fastened to the bottom 2, as by rivetedterminal 14. The upper reduced cylindrical end 15 of spindle 10 extendsthrough a bearing opening in housing cover 4 and is fixed to aninsulating block 15 arranged for use in manual rotation of spindle 10.in the form shown, the spindle end 15 is cemented in a socket in block16, and is further held in place by pin 17, the ends of which areinwardly spaced from the outer face of the block.

Block 16 advantageously includes an arrangement which facilitates manualoperation of the contact arm assembly 9, such as a screw driver slo Inthe form shown, a short rod 18 coaxial with spindle 10 is mounted onblock 16 as by cementing said rod in a socket in the block, and it mayalso be held in place by a short pin 19. The upper projecting end of rod18 is provided with a screw driver slot 20.

The spindle 10 carries a spring contact arm 21 within housing 1,slidably engaging resistance element 6. In the illustrated embodiment,arm 21 comprises a metal spring strip having an end mounted in aflat-faced recess 22 in spindle 10 by screw 23; and arm 21 may beannular in form with both ends held in recess 22 by screw 23 as shown. Aconvex contact stud 24 fixed to spring arm 21 bears against the innerface of resistance element 6.

An arrangement for limiting the rotation of the contact arm assembly 9may be provided. As shown, a laterally extending stop arm 25 is mountedon spindle 10, and has an upward extension 26 which engages a suitablestop on cover 4, such as stop stud 27 fitting tightly in an aperture insaid cover and projecting into the path of arm 25.

The disclosed arrangement may be used as either a rheostat or apotentiometer. For rheostat use the power circuit lines are soldered tothe external ends of terminal 14 and a terminal 7, the current passingthrough resistance 6, contact arm 21, spindle 10 and arm 13. When usedas a potentiometer, the power circuit lines are of course soldered toterminals 7, and the voltage take-off line to terminal 14. Since in bothcases spindle 10 is in the circuit, the insulating block 16 is arrangedto prevent contact by a screw driver or other object with spindle 10 orpin 17.

The disclosed construction eliminates any structure for making take-offconnections with the rotating contact arm assembly 9 inside the housing1, providing a compact simple construction suitable for practicalservice in very small sizes, rheostats of this type having an overalldiameter of only half an inch having been found satisfactory in use. Theconstruction also eliminates the use of screws engaging the plastichousing parts, such screws being objectionable and often impractical invery small sizes.

While a preferred embodiment of the invention has been shown anddescribed, modification thereof may be made without departing from theinvention.

We claim:

I. A variable resistor comprising a housing, a resistance element in thehousing, a rotatable contact unit slidably engaging the resistanceelement and including pivots extending through the housing at oppositesides, a terminal connected to the resistance element, and an externalterminal device frictionally engaging a pivot.

2. A variable resistor comprising a housing of insulating material, anarcuate resistance element in the housing, an external terminalconnected to an end of the resistance element mounted on the housing, ametal spindle in the housing having end portions extending through androtatably engaging the housing, a contact arm on the spindle slidablyengaging the resistance element, a contact element mounted externally onthe housing and engaging an end of the spindle, and a spindle rotatingdevice at the other end of the spindle.

3. A variable resistor as claimed in claim 2 in which the externallymounted contact element comprises a spring member having frictionalendwise engagement with the spindle end.

4. A variable resistor as claimed in claim 2 in which the resistanceelement is mounted on a side wall of the housing, and the contact armcomprises a curved spring arm laterally mounted on the spindle.

5. A variable resistor as claimed in claim 2 in which the spindlerotating device comprises a drive member of insulating material engagingan end of the spindle projecting from the housing.

6. A variable resistor as claimed in claim 2 in which the spindlerotating device comprises a connector block of insulating materialengaging an end of the spindleprojecting from the housing, and ametallic drive element fixed to the block and provided with a drive slotaligned with the spindle axis.

7. A variable resistor as claimed in claim 2 including a second terminalconnected to the other end of the resistance element, mounted on andextending through the housing.

8. A variable resistor as claimed in claim 2 including a stop armmounted on the spindle, and a stop projecting inwardly from the housingin the path of the stop arm.

9. A variable resistor as claimed in claim 2 including a stop armmounted on the spindle, a stop projecting inwardly from the housing inthe path of the stop arm, and a common mounting screw threaded into thespindle and engaging the contact arm and stop arm.

10. A miniature variable resistor comprising a housing of insulatingmaterial having a body and a cover held in place on the body by surfaceengagement therewith, an arcuate resistance element in the housing, anexternal terminal mounted on the housing and connected to the resistanceelement, a metal spindle in the housing having reduced cylindrical endportions rotatably fitting in openings in the housing, a spring contactarm mounted on the spindle and slidably engaging the resistance element,a spring contact arm mounted on the housing and frictionally engagingone end of the spindle, and a spindle rotating device at the other endof the spindle.

References Cited in the file of this patent UNITED STATES PATENTS

